The present invention concerns an apparatus for and a method of comminuting agglomerates and like material which is comminutable by mechanical blows, wherein the apparatus comprises a rotor drivable in rotation and having a plurality of blade-like comminuting tools which can be brought into contact with the material to be comminuted.
A corresponding apparatus is known for example from the prospectus ‘Lockerungsschleuder’ [‘Loosening centrifugal separator’] from VHV Anlagenbau which is provided for comminuting agglomerates of casting sand.
When processing systems of substances which are of very fine grain size or which contain binding agent, it is possible for example at the discharge of a silo or after a mixing or granulating process for a not inconsiderable part of the flow of material to accumulate in an unwanted fashion to constitute large agglomerates or lumps. Those agglomerates are generally of a low level of compression strength and can be relatively easily comminuted to the primary grain size of the particles or granules.
Frequently, such systems of substances are fed to a downstream-disposed filling and compacting process which produces the geometrical positive or negative mould for the end product. In that respect it is important for the mould to be uniformly filled. Large agglomerates and lumps can now interfere with the flow of substance in the filling process and thus result in defects in the definitive form of the product. For that reason the agglomerates and lumps should be comminuted to such an extent that they are of the desired primary grain size or granule size.
In particular, for comminuting lumps in the preparation of moulding sand, the above-mentioned comminuting apparatus which is referred to as the ‘Lockerungsschleuder’ is known, which can be mounted in the form of an independent attachment on a belt conveyor.
In that case the comminuting effect is implemented by way of relatively thick flails which are protected from wear and which are fixed in a spiral form on a horizontally extending shaft, at a relatively large lateral spacing. The rapidly rotating shaft is fixed transversely with respect to the conveyor direction of the material conveyor in such a way that the rotating flails are moved through the loose material, but do not involve any contact with the subjacent belt of the belt conveyor. The inside surfaces of the cover hood which is arranged relatively closely around the centrifugal separator unit is provided for example with wear-resistant anti-adhesion linings.
The problem of the known structure is that, particularly in the preparation of moulding sand, the material disposed on the belt conveyor is loosened out of the bed of material by the relatively thick flails and flung tangentially forwardly and upwardly in the direction of rotation of the rotating shaft. The lumps are comminuted by the beating loading of the flails and upon impact against the wall of the housing. It will be noted however that, in spite of the anti-adhesion coating, in particular transport in a vertical direction at high tangential speeds leads to severe caking of material in the catch housing.
The rotating flails must therefore be moved both through the relatively loose material being conveyed and also through the compacted caked material in the housing, and that leads to a high level of wear and unnecessarily high drive power levels at the rotating shaft.
In addition, by virtue of the relatively great lateral spacing between the flails, part of the material being conveyed can pass without full contact with the rotating flails between the comminuting unit, in a non-comminuted condition.